Crusher and a method of crushing material

ABSTRACT

A method of crushing material includes the steps of feeding a first flow of material to be crushed to a rotor rotating around a vertical axis, the rotor accelerating the first flow of material towards an impact wall section, and feeding a second flow of material to be crushed into the path of the accelerated first flow of material. The second flow of material is fed in a direction having a substantially tangential component in relation to the rotor, such that the second flow of material will have a substantially tangential component of movement in relation to the rotor when reaching the path of the first flow of material. A crusher is adapted to feed the second flow of material such that it will have a substantially tangential component of movement in relation to the rotor when reaching the path of the first flow of material.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to a vertical shaft impact crusher forcrushing material, said crusher comprising

a rotor for accelerating a first flow of material to be crushed,

a first feed means for vertically feeding the first flow of material tothe rotor,

a housing comprising a wall with a circumferential impact wall sectionagainst which the accelerated first flow of material may be crushed,

a second feed means for feeding a second flow of material to be crushedinto the path of the accelerated first flow of material.

The present invention further relates to a method of crushing material,said method comprising the steps of

feeding a first flow of material to be crushed to a rotor rotatingaround a vertical axis,

in said rotor accelerating said first flow of material towards an impactwall section of a housing surrounding the rotor,

feeding a second flow of material to be crushed into the path of theaccelerated first flow of material.

BACKGROUND ART

Vertical shaft impact crushers (VSI-crushers) are used in manyapplications for crushing hard material like rocks, ore etc. U.S. Pat.No. 3,154,259 describes a VSI-crusher comprising a housing and ahorizontal rotor located inside the housing. Material that is to becrushed is fed into the rotor via an opening in the top thereof. Withthe aid of centrifugal force the rotating rotor ejects the materialagainst the wall of the housing. On impact with the wall the material iscrushed to a desired size. The housing wall could be provided withanvils or have a bed of retained material against which the acceleratedmaterial is crushed.

To increase the amount of material crushed by the crusher two separatematerial flows could be fed to the crusher. A first material flow is fedto the rotor. The first material flow is accelerated by the rotor and isejected towards the housing wall. A second material flow is fed outsidethe rotor, i.e. between the rotor and the housing. This second materialflow is hit by the first material flow ejected by the rotor. Thus thefirst and second material flows are crushed against each other justoutside the rotor.

U.S. Pat. No. 2,012,694 to Runyan describes a crusher where a first flowof material is fed to the centre of a rotating rotor. A second flow ofmaterial is fed at the wall of a crusher housing via a feeder comprisingtwo spaced cones. At the housing wall the second flow of material is hitby the first flow of material ejected by the rotor.

U.S. Pat. No. 3,429,511 to Budzich describes a crusher where a firstflow of material is fed to the centre of a rotating rotor. A second flowof material is fed via a feeding gap extending around the rotor. Thesecond flow of material forms a continuous curtain of flowing materialcovering the pathway of the first flow of material just outside therotor. The first flow of material ejected by the rotor thus hits andcrushes the second flow of material.

U.S. Pat. No. 4,662,571 to MacDonald describes a crusher were a firstflow of material is fed to the centre of a rotating rotor. A second flowof material is fed into the path of the first material flow acceleratedby said rotor before said first material impacts against the crusherwall.

The above crushers do not to utilize the energy of the first flow ofmaterial in a very efficient way.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a crusher whichutilizes the energy of a first flow of material accelerated by a rotorin a more efficient way.

This object is achieved by a crusher according to the preamble andcharacterized in that

the second feed means comprises means for forming at least one hillsideon which the second flow of material may slide, the hillside having aslope being substantially tangential in relation to the rotor fordirecting the second flow of material in a direction having asubstantially tangential component in relation to the rotor, such thatthe second flow of material will have a substantially tangentialcomponent of movement in relation to the rotor when reaching the path ofthe first flow of material.

The present invention thus provides a second flow of material having asubstantially tangential component of movement. This improves thecrushing action and makes it possible to direct the second flow ofmaterial towards positions suitable for impact and away from theperiphery of the rotor and the internal structures, such as internalbeams of the crusher. The versatility of the crusher is improvedresulting in the ability to increase the throughput and to alter thesize distribution curve of the crushed product.

Preferably the wall of the housing comprises a circumferentialdistributing wall section forming part of the second feed means andbeing located above said impact wall section, the second feed meanscomprising means for feeding, in a first step, the second flow ofmaterial in a direction towards the distributing wall section, which isadapted to receive the second flow of material and to direct it againstthe impact wall section.

The distributing wall section makes it possible to give the second flowof material a desired velocity and the desired direction just before itis to enter the impact wall section.

Preferably the feed hopper means comprises an inner hopper and an outerhopper surrounding the inner hopper, said hoppers having a commonvertical axis substantially coinciding with the vertical axis of therotor, the inner hopper being provided with at least one outlet forallowing the second flow of material fed to the inner hopper to enter aspace formed between the inner and the outer hopper, an “L”-shapeddirection arm being fixed in the space between said hoppers just outsidesaid outlet to facilitate the building of a hillside of accumulatedmaterial, the hillside having a slope being tangential in relation tothe rotor for directing the second flow of material towards thedistributing wall section.

The inner and outer hopper provides an efficient way of distributing thedesired amount of material for forming the second flow of material. Thehillside formed on the direction arm provides an efficient base forgiving the second flow of material the desired direction without causingwear to internal components including the direction arm itself.

Preferably a horizontal leg of the “L”-shaped direction arm is pointingin the rotational direction of the rotor, such that any dust entrainedby the rotor in a direction having an upwardly directed component and acomponent being tangential in relation to the rotor will be hindered bya vertical leg of the direction arm.

The vertical leg of the direction arm will efficiently decrease the dustemission from the inner hopper. Thus expensive filtering means forfiltering emitted air may be omitted. It also becomes much easier toinspect the crusher during operation and to observe the amount ofmaterial forming the second flow of material.

Preferably the inner and outer hoppers have a polygonal shape as seenfrom above. The polygonal shape is preferable since it makes themanufacturing of outlets formed in the inner hopper and in particularhatches for covering said outlets much easier since they all can be madeflat. The polygonal shape also assists in reducing dust emissions fromthe crusher since the internal corners of the polygonal hoppers will getfilled with dust thereby creating dead pockets of retained dust, whichhelp absorbing the air flow created by the rotor. The polygonal shapealso helps deflecting the air streams swirling around inside thecrusher. The dead pockets of retained dust will also protect the innerand outer hopper from wear.

Preferably the second feed means further comprises the upper surface ofa ring fixed to the inner wall of said housing to separate thedistributing wall section from the impact wall section located below it.The ring provides a base for the distributing wall section and preventsany material from the impact wall section from bouncing up to thedistributing wall section. Also material from the distributing wallsection will be prevented from entering the impact wall section inplaces where it is not desired. The separation of the distributing wallsection from the impact wall section thus makes the crushing moreefficient and decreases wear on internal parts of the crusher.

Preferably the second feed means further comprises at least one verticalcollection plate extending radially with respect to the rotor, thecollection plate being fixed to the upper face of the ring at such alocation that a part of the second flow of material fed towards thedistributing wall section in said first step will accumulate against thecollection plate to form a hillside of material, the hillside having aslope being substantially tangential in relation to the rotor forgiving, in a second step, the remaining part of the second flow ofmaterial a substantially tangential component of movement in relation tothe rotor when reaching the path of the first flow of material. Thehillside formed will protect the internal parts, including thecollection plate and the upper surface of the ring from wear. Thehillside will also provide the desired direction for the second flow ofmaterial before the second flow of material enters the impact wallsection.

A further object of the present invention is to provide a method ofcrushing material which improve the utilization of the energy suppliedduring the crushing.

This object is achieved with a method according to the preamble andcharacterized in feeding the second flow of material in a directionhaving a substantially tangential component in relation to the rotor,such that the second flow of material will have a substantiallytangential component of movement in relation to the rotor when reachingthe path of the first flow of material. The inventive method makes itpossible to direct the second flow of material towards positionsattractive for impact and away from internal structures such as internalbeams of the crusher. Thus crushing action and utilization of crushingenergy is improved and wear inside the crusher is reduced.

Preferably the second flow of material is fed into the path of the firstflow of material adjacent to the impact wall section. An advantage withthis is that the second flow of material will, after being hit by thefirst flow of material, impact against the impact wall section. Thus thesecond flow of material will be crushed against the impact wall sectionand it will also be subjected to further hits of the first flow ofmaterial. The retention time of the second flow of material at theimpact wall section will thus be increased. This is a large advantageover prior art crushers where a second flow of material randomly fallsfreely between the rotor and the crusher wall. This random falling ofthe prior art crushers results in that a major part of a second flow ofmaterial will never be hit by the first flow of material. The randomlyfalling second flow of material of the prior art crushers will alsodeflect the first flow of material thus reducing or eliminating thecrushing against the crusher wall. Another advantage of the presentinvention is that the risk that the second flow of material accidentallyimpacts the rotor is decreased. Also the risk of the first flow ofmaterial accidentally rebounding against the rotor or other internalstructures after hitting the second flow of material is decreased. Thusthe wear on the crusher and in particular on the rotor is decreased.

Preferably the second flow of material is fed from a position adjacentto the axis of the rotor towards a wall of the housing in a directionhaving a substantial tangential component in relation to the rotor. Thecentral feeding of the material makes it possible to feed in oneposition and then divide the flow of material into a first flow ofmaterial and a second flow of material. The feeding towards the wallincreases the chance of placing the second flow of material in aposition suitable for best crushing performance. In particular thechance of the second flow of material reaching the path of the firstflow of material adjacent to the impact wall is improved.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will hereafter be described in more detail and withreference to the appended drawings.

FIG. 1 is three-dimensional section view and shows a rotor for aVSI-crusher

FIG. 2 is a three-dimensional view and shows the rotor of FIG. 1 withthe upper disc removed.

FIG. 3 shows the view of FIG. 2 as seen from above in a two dimensionalperspective.

FIG. 4 is a three dimensional view, partly in section, and shows avertical shaft impact crusher.

FIG. 5 is a section view and shows the crusher of FIG. 4.

FIG. 6 is a schematic section view and shows the build up of a bed ofretained material against an impact wall section.

FIG. 7 is a section view taken along the line VII-VII of FIG. 5.

FIG. 8 is a three dimensional view, partly in section, and shows thepathway of the second flow of material of the vertical shaft impactcrusher.

FIG. 9 is a top view, partly in section, and shows the pathway of thesecond flow of material of the vertical shaft impact crusher.

FIG. 10 is a side view showing a direction arm in detail.

FIG. 11 is a top view, partly in section, and shows the pathways of thefirst and the second flows of material according to an alternativeembodiment of the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

FIG. 1 shows a rotor 1 for use in a VSI-crusher. The rotor 1 has a roofin the form of an upper disc 2 having a top wear plate 3 and a floor inthe form of a-lower disc 4. The lower disc 4 has a hub 6, which iswelded to the disc 4. The hub 6 is to be connected to a shaft (notshown) for rotating the rotor 1 inside the housing of a VSI-crusher.

The upper disc 2 has a central opening 8 through which material to becrushed can be fed into the rotor 1. The upper disc 2 is protected fromwear by upper wear plates 10 and 12. The upper disc 2 is protected fromrocks impacting the rotor 1 from above by the top wear plate 3. As isbetter shown in FIG. 2 the lower disc 4 is protected from wear by threelower wear plates 14, 16 and 18.

The upper and lower discs 2, 4 are separated by and held together by avertical rotor wall which is separated into three wall segments 20, 22and 24. The gaps between the wall segments 20, 22, 24 define outflowopenings 26, 28, 30 through which material may be ejected against ahousing wall.

At each outflow opening 26, 28, 30 the respective wall segment 20, 22,24 is protected from wear by three wear tips 32, 34, 36 located at thetrailing edge of the respective wall segment 20, 22, 24.

A distributor plate 38 is fastened to the centre of the lower disc 4.The distributor plate 38 distributes the material that is fed via theopening 8 in the upper disc 2 and protects the lower disc 4 from wearand impact damages caused by the material fed via the opening 8.

During operation of the rotor 1 a bed 40 of material is built up insidethe rotor 1 against each of the three wall segments 20, 22, 24. In FIG.3 only the bed 40 located adjacent to the wall segment 20 is shown. Thebed 40, which consists of material that has been fed to the rotor 1 andthen has been trapped inside it, extends from a rear support plate 42 tothe wear tips 32, 34, 36. The bed 40 protects the wall segment 20 andthe wear tips 32, 34, 36 from wear and provides a proper direction tothe ejected material. The dashed arrow A describes a typical passage ofa piece of rock fed to the rotor 1 via the central opening 8 and ejectedvia the outflow opening 26. The arrow R indicates the rotationaldirection of the rotor 1 during operation of the VSI-crusher.

Each wall segment 20, 22, 24 is provided with a cavity wear plate 44,46, 48, each preferably having three cavity wear plate portions. Thecavity wear plates 44, 46, 48 protect the rotor 1 and in particular thewear tips 32, 34, 36 from material rebounding from the housing wall andfrom ejected material and airborne fine dust spinning around the rotor1.

In FIG. 4 a vertical shaft impact crusher 50 is shown. The rotor 1 islocated inside a housing 52 of the crusher 50. At the top of the crusher50 a feed hopper means 54 is located. The feed hopper means 54 has ahexagonal inner hopper 56 and a hexagonal outer hopper 58. A roof, notshown in FIG. 4, seals a space 60 formed between the inner hopper 56 andthe outer hopper 58 from above. The inner hopper 56 is provided with sixoutlets 62, each outlet 62 being located at a side of the hexagonalinner hopper 56. Each outlet 62 is provided with a movable hatch 64. Themovable hatch 64 may be placed in three different positions on the innerhopper 56 to obtain a desired open area of the respective outlet 62. An“L”-shaped direction arm 66 is fixed between the inner hopper 56 and theouter hopper 58 adjacent to each outlet 62. Below the inner hopper 56 acentral feeding cylinder 68 is placed. The feeding cylinder 68 is fixedto the inside of the wall 70 of the housing 52 with the aid of threebeams of which only the beam 72 is shown in FIG. 4.

A circumferential distributing wall section 74 is located at the samelevel as the feeding cylinder 68. Below the distributing wall section 74and on the same level as the rotor 1 a circumferential impact wallsection 76 is located. A cavity ring 78 separates the distributing wallsection 74 from the impact wall section 76. A number of verticalcollection plates 80 which extend radially with respect to the rotor 1are fixed to the upper surface 82 of the ring 78.

A bed retention ring 84 is located at the bottom of the crusher 50. Anumber of bed support plates 86 are located between the bed retentionring 84 and the cavity ring 78. A throttle means 88, partly shown inFIG. 4, is located between the inner hopper 56 and the feeding cylinder68.

FIG. 5 shows that the throttle means 88 controls a sliding throttle 90located at the bottom 92 of the inner hopper 56. Material to be crushedis fed to the inner hopper 56 in the direction of the arrow M. The roof94 prevents material from falling directly into the space 60 between theinner hopper 56 and the outer hopper 58. The roof 94 also prevents dustfrom flowing out of the top of the crusher 50. The opening position ofthe sliding throttle 90 determines the amount of material forming afirst flow of material M1 that will reach the rotor 1 via an inlet 96 atthe bottom 92 of the inner hopper 56 and the feeding cylinder 68 inrelation to the amount of material forming a second flow of material M2that will reach the space 60 via the outlets 62.

FIG. 6 shows how the rotor 1, being rotated with the aid of a not shownshaft connected to the hub 6, will accelerate the first flow of materialM1 against the impact wall section 76. Quite soon after the crusheroperation has been started some crushed material will accumulate againstthe impact wall section 76 to form a wall bed 98 of retained material asshown in FIG. 6. The bed support plates 86, the bed retention ring 84and the cavity ring 78 will support the bed and provide a desired shape.The first flow of material M1 will be accelerated by the rotor 1 andimpact against the wall bed 98 of retained material. Thus a so calledautogenous crushing is obtained wherein the first flow of material M1 iscrushed against a wall bed 98 formed from part of the materialpreviously crushed.

FIG. 7 shows, as seen from above, the sliding throttle 90 and the inlet96 at the bottom 92 of the inner hopper 56. An inspection hatch 100makes it possible to inspect the rotor 1 and perform maintenance insidethe crusher 50. In FIG. 7 the roof 94 has been partially removed tovisualize an advantageous effect of the polygonal hoppers 56, 58.Between two adjacent direction arms 66 a dead pocket 101 of accumulatedmaterial has been built up during crusher operation. The dead pocket101, being formed between the polygonal hoppers 56 and 58, protects thedirection arm 66, the roof 94 and the hoppers 56, 58 against wear causedby the second flow of material M2.

The operation of the crusher 50 will now be described in more detailwith reference to FIG. 8 to 10. As described with reference to FIG. 5the feed of material M is divided in a first flow of material M1 and asecond flow of material M2. The second flow of material M2 passes out ofthe outlets 62 and lands on the direction arms 66. Each direction arm 66has, as is best shown in FIG. 10, a vertical leg 102 and a horizontalleg 104. At an end of the horizontal leg 104 a projection 106 has beenwelded. The second flow of material M2 will initially build a hillside108 of material on the direction arm 66. Once the hillside 108 is inplace, after few minutes of crusher operation, the second flow ofmaterial M2 will slide on the hillside 108 thus obtaining a movementhaving a substantially tangential component in relation to the rotor 1,as can be seen from FIG. 8 and FIG. 9. The second flow of material M2will thus in this first step be directed towards the distributing wallsection 74. At the location of the distributing wall section 74 wherethe second material flow would impinge the wall section 74 thecollection plate 80 is located. During the first minutes of crusheroperation the second flow of material M2 will build a second hillside110 of material against the collection plate 80 and the upper surface 82of the cavity ring 78 as is best shown in FIG. 8. After the secondhillside 110 has been established the rest of the second flow ofmaterial M2 will, in a second step, slide on the second hillside 110.The second material flow M2 will thus, in this second step, obtain amovement having a substantially tangential component in relation to therotor 1. The second material flow M2 will then pass on down into aposition adjacent to the impact wall section 76. Adjacent to the impactwall section 76 the second flow of material M2 having a movement with asubstantially tangential component will be hit by the first flow ofmaterial M1 ejected by the rotor. When the second flow of material M2 ishit by the first flow of material M1 it will be forced against the wallbed 98. Since the second flow of material M2 is fed adjacent to theimpact wall section 76 the second flow of material M2 will land on thewall bed 98 either directly or after being hit by the first flow ofmaterial M1 and be exposed to the impact of the first flow of materialM1 for a long period of time thus achieving an efficient crushing. Itwill be appreciated that, as clearly demonstrated in FIG. 6, any part ofthe second flow of material M2 that by accident is not immediately hitby the first flow of material M1 will also land on the wall bed 98 thusgetting more chances of being hit by the first flow of material M1. Thiseffect is enhanced by the fact that the second flow of material M2 isgiven a tangential component of movement by the second hillside 110 andis thus directed against the wall bed 98. Thus any part of the secondflow of material M2 that is not hit by the first flow of material M1 (asillustrated in FIG. 9) will instead directly impact the wall bed 98 andbe retained there for some time. The increased retention time of thesecond material flow M2 on the wall bed 98 is particularly importantsince the first flow of material M1 will appear to be pulsed whenleaving the rotor 1. Since the rotor 1 is rotated and the first flow ofmaterial M1 is ejected through the three outflow openings 26, 28, 30 ofthe rotor 1, a given portion of the wall bed 98 will become hit by thefirst flow of material M1 three times per each revolution of the rotor1, i.e. if the rotor rpm is 1500, a given portion of the wall bed 98will become hit 3×1500=4500 times per minute. The increased retentiontime of the second flow of material M2 on the wall bed 98 ensures thatthe second flow of material M2 will become hit by the first flow ofmaterial M1 before leaving the crusher. In fact the second flow ofmaterial M2 will be hit many times by the first flow of material M1 thusensuring an efficient crushing. FIG. 8 further shows that the internalbeam 72 has such a location in relation to the collection plate 80 thatthe beam 72 is not hit by the second flow of material M2.

As is indicated with a dashed arrow in FIG. 9 the movement of the firstflow of material M1 will have a substantially tangential component.Since the second flow of material M2 has a movement with a substantiallytangential component having the opposite direction, the first flow ofmaterial M1 will impact the second flow of material M2 in a head-oncollision thus further improving the crushing action. The fact that thefirst and second flows of material M1, M2 travel in opposite directionsbefore impacting each other provides an optimum initial impact energy.

From FIG. 10 another important aspect of the direction arm 66 is shown.The rotation of the rotor 1 will cause entrainment of dust particles.The particles will swirl along the rotational direction, shown with adashed arrow R in FIG. 10, of the rotor 1 and move up an down in thecrusher 50. The vertical leg 102 of the direction arm 66 and thehorizontal leg 104 pointing in the direction of the rotational directionR will however deflect the dust particles and force them down into thecrusher 50, as indicated with an arrow D in FIG. 10. Thus the dustemissions from the crusher 50 will be substantially reduced thanks tothe direction arm 66. The dead pocket 101 built up against the verticalleg 102 improves the deflection of the dust particles and also protectsthe vertical leg 102, the roof 94, the inner hopper 56 and the outerhopper 58 (not shown in FIG. 10) from wear. The polygonal shapes of theinner hopper 56 and the outer hopper 58 will tend to diffuse the airrotating inside the crusher. The polygonal shape thus assists indecreasing the dust emission from the crusher.

It will be appreciated from FIG. 9 that a minor part of the second flowof material M2 sliding on the hillside 108 may not reach thedistributing wall section 74 and the second hill 110. This minor part ofthe second flow of material M2 will, however, also have a movement witha substantially tangential component and will be directed directlytowards the impact wall section 76 where it is hit by the first flow ofmaterial M1.

FIG. 11 illustrates an alternative embodiment of the invention. Avertical shaft impact crusher 150, similar to the crusher 50 shown inFIG. 4-10, is equipped with a rotor 111. The rotor 111 is similar to therotor 1 that is illustrated in FIG. 1-3 but is adapted to be rotated inthe opposite direction R′, i.e. clockwise. The rotor 111 will thusproduce a first flow of material M1′ that has another direction than thefirst flow of material M1 shown in FIG. 9. As is indicated with a dashedarrow in FIG. 11 the movement of the first flow of material M1′ willhave a substantially tangential component. Since the second flow ofmaterial M2 has a movement with a substantially tangential componenthaving the same direction, the first flow of material M1′ will impactthe second flow of material M2 in a “from behind” collision. The factthat the first and second flows of material M1′, M2 travel in the samedirection before impacting each other provides a reduced impact actioncompared to the head-on collision illustrated in FIG. 8-9 but instead animproved grinding and attrition action. The grinding and attritionaction provides an improved shape, i.e. an improved roundness, to thematerial that is fed to the crusher. Thus the embodiment illustrated inFIG. 11 is particularly suitable for cases where the material to becrushed requires a moderate to low reduction in size but an increasedroundness. It will be appreciated that an alternative way of achievingthe “from behind” collision is to keep the rotor 1 having the directionof rotation R in the crusher and instead alter the direction of thedirection arm 66 and change the position of the collection plate 80 toobtain a second flow of material having the opposite direction comparedto the second flow of material M2 shown in FIGS. 9 and 11.

It will be appreciated that numerous modifications of the embodimentsdescribed above are possible within the scope of the appended claims.

In an alternative embodiment of the invention only the hillside 108 isused. In such an embodiment the hillside 108 formed on the direction arm66 directs the second flow of material M2 directly towards the impactwall section 76 without going via the distributing wall section, whichmay be omitted in this alternative embodiment. The second flow ofmaterial M2 thus having a movement with a substantially tangentialcomponent will reach the path of the first flow of material M1 adjacentto the impact wall section 76 and be subjected to multiple hits by thefirst flow of material M1 at the wall bed 98 just like in the embodimentdescribed above.

In still another embodiment of the invention only the hillside 110 isused. In such an embodiment the second flow of material M2 is droppedvertically on the upper surface 82 of the cavity ring 78. A collectionplate 80 located on the surface 82 will provide a basis for theaccumulation of a hillside 110. The second flow of material M2 fallingvertically on the hillside 110 will slide on the hillside 110 thusobtaining a movement having a substantially tangential component inrelation to the rotor 1. The second flow of material M2 will then enterthe impact wall section 76 and be crushed in accordance with what hasbeen described above.

The inner and outer hopper may in alternative embodiments have otherpolygonal shapes such as square, pentagonal etc. The inner and outerhoppers may also be circular. The polygonal shape is preferable since itmakes the manufacturing of the outlets and in particular the hatchesmuch easier since they can be made flat. The polygonal shape alsoreduces the wear on the hopper and the dust emission from the crusher.

In an alternative embodiment the horizontal leg 104 of the direction arm66 may have a length which is adjustable. Thus the length of thehorizontal leg could be adjusted to accommodate different feed materialtypes and sizes. The length of the horizontal leg could also be adjustedto optimise the reduction of dust emission from the crusher.

Above it has been described that the hillsides 108, 110 on which thesecond flow of material M2 slides are formed by material accumulating onthe direction arm 66 and against the cavity ring 78 and the collectionplate 80 respectively. It is however also possible to form aprefabricated hillside of e.g. a steel sheet, a ceramic tile or asimilar plate, said hillside having a desired tangential slope inrelation to the rotor immediately from the start of the crusher.However, hillsides 108 and 110 that are made up of accumulated materialhave the advantage of avoiding the wear problems that would beassociated with prefabricated hillsides made of a steel sheet or another material.

1. A vertical shaft impact crusher for crushing material, said crushercomprising: a rotor for accelerating a first flow of material to becrushed, a first feed means for vertically feeding the first flow ofmaterial to the rotor, a housing comprising a wall with acircumferential impact wall section against which the accelerated firstflow of material may be crushed, a second feed means for feeding asecond flow of material to be crushed into the path of the acceleratedfirst flow of material, wherein the second feed means comprises meansfor forming at least one hillside on which the second flow of materialmay slide, the hillside having a slope being substantially tangential inrelation to the rotor for directing the second flow of material in adirection having a substantially tangential component in relation to therotor, such that the second flow of material will have a substantiallytangential component of movement in relation to the rotor when reachingthe path of the first flow of material.
 2. A crusher according to claim1, wherein the wall of the housing comprises a circumferentialdistributing wall section forming part of the second feed means andbeing located above said impact wall section, the second feed meanscomprising feed hopper means for feeding, in a first step, the secondflow of material in a direction towards the distributing wall section,which is adapted to receive the second flow of material and to direct itagainst the impact wall section.
 3. A crusher according to claim 2,wherein the feed hopper means comprises an inner hopper and an outerhopper surrounding the inner hopper, said hoppers having a commonvertical axis substantially coinciding with the vertical axis of therotor, the inner hopper being provided with at least one outlet forallowing the second flow of material fed to the inner hopper to enter aspace formed between the inner and the outer hoppers, an “L”-shapeddirection arm being fixed in the space between said hoppers just outsidesaid outlet to facilitate the building of a hillside of accumulatedmaterial, the hillside having a slope being tangential in relation tothe rotor for directing the second flow of material towards thedistributing wall section.
 4. A crusher according to claim 3, wherein ahorizontal leg of the “L”-shaped direction arm is pointing in therotational direction of the rotor, such that any dust entrained by therotor in a direction having an upwardly directed component and acomponent being tangential in relation to the rotor will be hindered bya vertical leg of the direction arm.
 5. A crusher according to claim 3,wherein the inner and outer hoppers have a polygonal shape as seen fromabove.
 6. A crusher according to claim 2, wherein the second feed meansfurther comprises the upper surface of a ring fixed to the inner side ofthe wall of said housing to separate the distributing wall section fromthe impact wall section located below it.
 7. A crusher according toclaim 6, wherein the second feed means further comprises at least onevertical collection plate extending radially with respect to the rotor,the collection plate being fixed to the upper face of the ring at such alocation that a part of the second flow of material fed towards thedistributing wall section in said first step will accumulate against thecollection plate to form a hillside of material, the hillside having aslope being substantially tangential in relation to the rotor for givingthe second flow of material a substantially tangential component ofmovement in relation to the rotor when reaching the path of the firstflow of material.
 8. A method of crushing material, said methodcomprising the steps of feeding a first flow of material to be crushedto a rotor rotating around a vertical axis, in said rotor, acceleratingsaid first flow of material towards an impact wall section of a housingsurrounding the rotor, feeding a second flow of material to be crushedinto the path of the accelerated first flow of material wherein feedingthe second flow of material in a direction having a substantiallytangential component in relation to the rotor, such that the second flowof material will have a substantially tangential component of movementin relation to the rotor when reaching the path of the first flow ofmaterial.
 9. A method according to claim 8, wherein the second flow ofmaterial is fed into the path of the first flow of material adjacent tothe impact wall section.
 10. A method according to claim 8, wherein thesecond flow of material is fed from a position adjacent to the axis ofthe rotor towards a wall of the housing in a direction having asubstantial tangential component in relation to the rotor.